a) Field of the Invention
This invention relates to an armature core for use with small-size motors. In particular, the invention relates to an armature core for use with small-size motors having a core element in an annular form that is made of a magnetic material and an insulating layer that is formed on the surface of the core element to prevent incomplete insulation from winding coils. Also formed on the core element are a plurality of salient poles and rib portions that are formed on the salient poles and around which the coils are wound.
b) Background of the Related Art
A method conventionally used to form the insulating layer is by an electrostatic coating process in which a resin powder deposited on the surface of the core element by static electricity is fired so as to consolidate the resin powder by high-frequency heating. An armature core insulated by this method, or which has an insulating layer formed on the surface of the core element, is generally indicated by 51 in FIG. 7. Coils 54 are wound around rib portions 55 formed on a plurality of salient poles, thereby providing a core winding assembly. This core winding assembly is coupled via spacers 52 to a circuit assembly composed of a circuit for driving a small-size motor and a substrate 53 to be equipped with this drive circuit. Thus, the core winding assembly and the circuit assembly combine together to form the stator assembly of the motor.
The spacers 52 are provided between the core winding assembly and the circuit assembly in order to avoid accidental contact between those assemblies that would otherwise occur during the formation of the stator assembly.
The insulating layer of the armature core that is formed by the conventional electrostatic coating process comprises a resin powder deposited by static electricity and suffers from various disadvantages such as surface asperities, uneven thickness and variations in thickness from one lot to another. These phenomena have caused a failure to wind coils in alignment in a subsequent step. Coils are said to be wound in alignment if, as shown in FIG. 4, adjacent turns 3 are wound around rib portions 24 on salient poles without forming any gaps or overlapping with each other.
Unexamined Published Japanese Utility Model Application No. 34851/1989 describes an armature core that comprises laminated core elements and which has an insulating resin layer formed by molding at both an upper and a lower end face in the direction of lamination of those core elements, whereby the salient poles on the core elements are entirely covered with the insulating resin. This technique, however, has had the problem that in the absence of a relief for the resin during its molding, the core elements will be pulled by the resin to experience warpage.